The invention relates generally to magneto powered capacitive discharge ignition systems for internal combustion engines, and more particularly, to such ignition systems including voltage regulator circuits for regulating the voltage developed on a charge capacitor. Attention is directed to ignition systems disclosed in the following U.S. Pat. Nos.: Cavil 4,074,669 issued Feb. 21, 1978; Farr 3,490,426 issued Jan. 20, 1970; London 3,240,198 issued Mar. 15, 1966; Beuk 3,669,086 issued June 13, 1972.
Attention is also directed to Burke, U.S. Pat. No. 4,001,537 issued Jan. 4, 1977, Tolworthy, U.S. Pat. No. 3,714,546, issued Jan. 30, 1973 and to an advertisement including a circuit description of the Allison "OPTO XR-700" ignition system manufactured by Allison Automotive Co. located at 1267 East Edna Plaza, Covina, California. The Burke and Tolworthy patents and the Allison circuit description relate to semiconductor devices utilized in power or voltage regulator circuits.
Typical prior voltage regulator circuits utilized in magneto powered capacitive discharge ignition systems have employed SCR's or transistors triggered by zener diodes, or employed one or more series connected zener diodes, connected directly in parallel with the charge capacitor. Ideally, these regulator circuits prevent overcharging of the charge capacitor by limiting the magnitude of the voltage at the positive terminal of the charge capacitor to the zener diode breakdown voltage. The components of such voltage regulator circuits, however, are subject to high power dissipation and failure due to component tolerance and excessive voltage on the charge capacitor, or due to high magnitude voltage and current surges occurring during discharge of the charge capacitor through the primary winding of the ignition coil.
Another such typical prior voltage regulator circuit is disclosed in Farr, U.S. Pat. No. 3,490,426, wherein a zener diode is connected in parallel across the magneto charge coil upstream of a blocking diode. The zener diode in this arrangement limits the positive voltage output of the magneto charge coil to the zener diode breakdown voltage, but shunts the negative output of the charge coil, thereby undesirably reducing the speed at which charge capacitor charges, and consequently, the magnitude of the voltage developed thereon. Further the zener diode in the Farr arrangement is subject to excessive magneto charge coil voltage, due to component tolerance, or due to an open circuit fault in the ignition triggering SCR or the primary winding ignition coil circuits. As a result of such excessive voltage, the zener diode in Farr is subject to excessive power dissipation and consequent failure.
As noted above, typical prior art voltage regulator circuits utilized in magneto powered capacitive discharge ignition systems have been subject to zener diode and other voltage regulator component failures, and hence, have proven unreliable. The failure of such prior art voltage regulator circuits has been particularly serious and troublesome because it results in the failure of the ignition system, and more importantly, because it results in the failure of the internal combustion engine and vehicle which the ignition system controls. Such voltage regulator failure requires an annoying and costly replacement or repair of the voltage regulator circuit before the ignition system and hence, the internal combustion engine and vehicle, can again be made operative.